Microfabrication refers to the fabrication of desired structures of micrometer scales and smaller. Microfabrication may involve etching of and/or deposition on a substrate (and possibly etching of and/or deposition on a film deposited on the substrate) to create the desired microstructure on the substrate (or film on the substrate). As used herein, the term “patterning a substrate” or similar encompasses all such etching of/deposition on a substrate or substrate film.
Wet etching involves using a liquid etchant to selectively dislodge parts of a film deposited on a surface of a substrate and/or parts of the surface of substrate itself. The etchant reacts chemically with the substrate/film to remove parts of the substrate/film that are exposed to the etchant. The selective etching may be achieved by depositing a suitable protective layer on the substrate/film that exposes only parts of the substrate/film to the chemical effects of etchant and protects the remaining parts from the chemical effects of the etchant. The protective layer may be formed of a photoresist or other protective mask layer. The photoresist or other mask may be deposited over the whole of an etching surface area then exposed and developed to create a desired “image”, which is then engraved in the substrate/film by the etchant to form a three dimensional structure.
Dry etching involves selectively exposing a substrate/film (e.g. using a similar photoresist mask) to a bombardment of energetic particles to dislodge parts of the substrate/film that are exposed to the particles (sometimes referred to as “sputtering”). An example is ion beam etching in which parts are exposed to a beam of ions. Those exposed parts may be dislodged as a result of the ions chemically reacting with those parts to dislodge them (sometimes referred to as “chemical sputtering”) and/or physically dislodging those parts due to their kinetic energy (sometimes referred to as “physical sputtering”).
In contrast to etching, deposition—such as ion-beam deposition or immersion-based deposition—involves applying material to rather than removing material from a substrate/film.